High frequency semiconductor device

ABSTRACT

A structure for preveting MMICs (Monolithic Microwave Integrated Circuits) from the deterioration in the high-frequency transmission characteristics thereof, which is resulted from mechanical pressure applied to the pads during the wire-bonding thereto for external connection. The structure includes a groove provided in the surface of the interlayer insulation film around each of the pads. The line conductor for transmitting high-frequency signals is free from the peeling off or bending thereof, which is caused by the deformation in the interlayer insulation films during when the mechanical pressure applied to the pads, and thus, the change in the transmission characteristics of the line conductor can be minimized, and the reliability of MMICs can be improved.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to MMIC (Monolithic MicrowaveIntegrated Circuit) having a wave guide for high-frequency signaltransmission.

[0003] 2. Description of the Related Art

[0004] Being different from conventional silicon integrated circuits,MMICs comprising high-speed semiconductor devices such as thatrepresented by HEMT (High Electron Mobility Transistor) or HBT (HeteroBipolar Transistor) necessarily include a wave guide as the innertransmission line for high-frequency signals. Micro-strip lines aregenerally used as the high-frequency signal wave guide, because of theirstable line characteristics and low dispersion characteristics whichmeans that the frequency dependency of propagation constant is weak.FIG. 1 shows an MMIC having conventional micro-strip lines, inparticular, a three-dimensional MMIC having micro-strip lines composedof multi-layered line conductors.

[0005] As shown in FIG. 1, the MMIC having a conventional multi-layeredstructure includes ground plate 3 formed on the semiconductor substrate1 with the insertion of surface insulation film 2 therebetween, andground plate 3 forms micro-strip lines together with line conductors 5each formed on each of interlayer insulation films 4, respectively. Inaddition to line conductors 5, pad 6 for the external connection isprovided on the most upper interlayer insulation film 4.

[0006] The MMIC having multi-layered high-frequency micro-strip lines asexplained with reference to FIG. 1 features that it is suited to highdensity integration, compared to MMICs having line conductors disposedin a single layer.

[0007] However, none of reports appear to discuss the reliability ofsuch multi-layered high-frequency micro-strip lines so far.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a structureof three-dimensional MMIC designed by taking reliability intoconsideration.

[0009] In three-dimensional MMICs, the interlayer insulation films arecomposed of a resin (organic) insulating material such as polyimide orbenzocyclobutene (BCB).

[0010] The interlayer insulation film of such resin insulating materialis relatively soft and is apt to deform, when a pressure is appliedthereto. Pads, for instance, are subjected to a mechanical shock by thetip of a bonding tool during wire bonding thereto, and deformation iscaused in the interlayer insulation film around there.

[0011] As a result, line conductor 5 on the most upper interlayerinsulation film would peel off or bends. When wire bonding is over andapplication of the pressure by the bonding tool is removed, theinterlayer insulation film can recover from the deformation itself.However, the line conductor that is once peeled off or bent cannotrestore, and results in the change of its high-frequency transmissioncharacteristics.

[0012] In the present invention, a groove is provided in the interlayerinsulation film adjacent to the pad, for relaxing the influence of thedeformation given during wire bonding processes.

[0013]FIG. 2 shows the essential concept of the present inveniton. Asshown in the drawing, groove 7 is provided adjacent to pad 6, and thus,PAD REGION and WIRING REGION are physically separated each other atleast by the groove near the respective surfaces thereof. Accordingly,even when pad 6 is subjected to wire bonding processes, aforesaiddeformation caused in the interlayer insulation film by the pressureapplied to pad 6 is relaxed by the shape effect of groove 7, and theinfluence of the deformation on WIRING REGION can be alleviated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a cross-sectional view of an MMIC having conventionalmicro-strip lines;

[0015]FIG. 2 is a cross-sectional view for explaining the essentialconcept of the present inveniton;

[0016]FIG. 3 is a plan view showing an embodiment of the presentinveniton;

[0017]FIG. 4 is a cross-sectional view taken on segment line A-A′ inFIG. 3;

[0018]FIG. 5 is a plan view showing another embodiment of the presentinveniton,

[0019]FIG. 6 is a plan view showing futher another embodiment of thepresent inveniton; and

[0020]FIG. 7 is a plan view showing still another embodiment of thepresent inveniton.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Embodiments of the present invention will be explained in thefollowing with reference to drawings.

[0022]FIG. 3 is a plan view of an embodiment of three-dimensional MMICacconding to the present inveniton, and FIG. 4 is a cross-sectional viewtaken on segment line A-A′ in FIG. 3.

[0023] In this embodiment, a compound semiconductor substrate of GaAs isused, in which active devices such as FETs are formed, and a surfaceinsulation film 2 of silicon nitride, for instance, is formed on thesurface of the substrate. A ground plate 3 to be connected to groundpotential is formed on the surface insulation film 2, and a plurality ofinterlayer insulation films 4 are formed thereon. The interlayerinsulation films are composed of polyimide or benzocyclobutene (BCB). Oninterlayer insulation films 4, line conductors 5 each having apredetermined pattern are formed, respectively. Each of line conductors5 is formed from gold (Au) by using sputtering or vacuum deposition andpatterned by using ion milling or lift-off technologies.

[0024] In this embodiment, groove 7 is formed to surround pad 6, exceptthe side of pad 6, which is facing the edge of semiconductor substrate1. Groove 7 is formed by using methods like etching. The depth of groove7 can substantially be optional, such as that the same as the thicknessof one of the interlayer insulation films, or deeper or shallower interms of the thickness. In this embodiment, groove 7 is formed to extendinto plural interlayer insulation films 4.

[0025] Pad 6 is formed in the same process as that for line conductor 5on the most upper interlayer insulation film 4, and is connected viathrough hole 8 to another line conductor 5 extending immediatelythereunder, to be used for internally supplying a potential.

[0026] According to this embodiment, the deformation caused in theinterlayer insulation film during the wire bonding to pad 6 is relaxedby groove 7, and line conductor 5 on the most upper interlayerinsulation film 4 can be prevented from peeling off or bending ofitself.

[0027] In this embodiment, pad 6 is formed adjacent to the edge of thesemiconductor substrate chip, and groove 7 is not provided at theperiphery of the semiconductor substrate chip where none of lineconductors is provided. However, groove 7 may be provided along whole ofthe periphery, according to need.

[0028]FIG. 5 is a plan view for explaining another embodiment of thepresent inveniton. In this embodiment, line conductor 5 is provided onthe most upper interlayer insulation film on which pad 6 is provided,and is connected to pad 6, as shown in the drawing. Accordingly, aconnection portion 9 where groove 7 is not formed is provided forallowing line conductor 5 to pass therethrough.

[0029] Also in this embodiment, the deformation of the interlayerinsulation film caused by bonding pressure to pad 6 is relaxed by groove7, and the shape change which would propagate into WIRING REGION can bereduced. A portion of PAD REGION is connected with WIRING REGION throughconnection region 9. However, the deformation by the bonding pressureapplied to pad 6 is almost interrupted by the discontinuity provided inthe interlayer insulation films by groove 7, and accordingly, lineconductor 5 connected to pad 6 is hardly affected by the influence ofthe deformation.

[0030]FIG. 6 is a plan view for explaining futher another embodiment ofthe present inveniton.

[0031] In this embodiment, plural grooves 7 are provided. Also in thisembodiment, the deformation by the bonding pressure is relaxed bygrooves 7 as in the previous embodiments, and the change in the shape ofthe insulation film in WIRING REGION is reduced.

[0032]FIG. 7 is a plan view for explaining still another embodiment ofthe present inveniton. The structure employed in this embodiment is thata ring-shaped groove 7 is provided between a region for forming pads 6and a region for forming line conductors (not shown) on semiconductorchip 100.

[0033] Each of pads 6 itself is solid because of its larger areacompared with line conductors, and hardly peel off or deform, even ifdeformation is caused at a pad 6 during bonding process and reachesneibhoring pads 6.

[0034] In this embodiment, the groove has a rectangular shape in itsplan view, however, there is no particular limitation in the shape ofthe groove, as far as it is intended to provied a discontinuity at leastin the most upper interlayer insulation film. And also, there is noparticular limitation in the depth and the shape of the bottom of thegroove (e.g. a groove having U- or V-shaped cross-section).

[0035] According to the present invention, as explained above, thedeformation caused in the interlayer insulation film during bondingprocess hardly propagate into WIRING REGION, and line conductors on themost upper interlayer insulation film can be prevented from theirpeeling off from the interlayer insulation film and the change in theirhigh-frequency transmission characteristics.

What is claimed is:
 1. A high-frequency semiconductor device comprising:a ground plate provided on a semiconductor substrate; a plurality ofline conductors provided on said ground plate, forming a multiple layerstructure with interlayer insulation films intervening therebetween thatis composed of a resin insulating material; a pad provided on most upperone of said interlayer insulation films; and a groove provided in saidmost upper one of said interlayer insulation films and between said padand said line conductor on said most upper one of said interlayerinsulation films.
 2. A high-frequency semiconductor device as set forthin claim 1, wherein said groove is disposed to surround said pad.
 3. Ahigh-frequency semiconductor device as set forth in claim 1, whereinsaid groove is partially disposed in a region between said pad and saidline conductor on said most upper one of said interlayer insulationfilms.
 4. A high-frequency semiconductor device as set forth in claim 3,wherein said pad is disposed in a peripheral region along an edge ofsaid semiconductor substrate, and said groove is partially disposed in aregion on said semiconductor substrate except said peripheral region. 5.A high-frequency semiconductor device as set forth in claim 3, wherein aplurality of said grooves are provided in said most upper one of saidinterlayer insulation films.
 6. A high-frequency semiconductor device asset forth in claim 1, comprising a through-hole provided in said mostupper one of said interlayer insulation films on which said pad isprovided, and said pad being connected to a potential via saidthrough-hole.
 7. A high-frequency semiconductor device as set forth inclaim 1 includes a line conductor connected to said pad on said mostupper one of said interlayer insulation films, and wherein said grooveis provided in a region except a connection portion for said lineconductor connected to said pad passing therethrough.
 8. Ahigh-frequency semiconductor device as set forth in claim 1, whereinsaid groove is provided to have a ring shape within said semiconductorsubstrate, and said pad is provided on said most upper one of saidinterlayer insulation films outside said ring shaped groove.
 9. Ahigh-frequency semiconductor device as set forth in claim 1, whereinsaid interlayer insulation film is composed of a polyimid orbenzocyclobutene.